Aqueous acidic plating baths for electrolytic deposition of copper are used for manufacturing printed circuit boards and IC substrates where fine structures like trenches, through holes (TH), blind micro vias (BMV) need to be filled with copper. Another application which is becoming more important is filling through glass vias, i.e. holes and related recessed structures in glass substrates with copper or copper alloys by electroplating. A further application of such electrolytic deposition of copper is filling of recessed structures such as through silicon vias (TSV) and dual damascene plating or forming redistribution layers (RDL) and pillar bumps in and on semiconducting substrates. For redistribution layers (RDL) and pillar bumps, a photoresist mask is used to define the microstructures to be filled with electrolytic copper. Typical dimensions for RDL patterns are 100 to 300 μm for pads and 5 to 30 μm for contact lines; copper thicknesses are usually in the range of 3 to 8 μm or in some cases up to 10 μm. Deposit thickness homogeneity within the microstructure (within profile uniformity=WIP), within the chip/die area (within die uniformity=WID) and within the wafer (within wafer uniformity=WIW) are critical criteria. Pillar bumping applications require copper layer thicknesses of about 10 to 100 μm. The pillar diameters are typically in the range of 20 to 80 or even up to 100 μm. In-die non-uniformity and within-bump non-uniformity values of less than 10% are typical specifications.
The patent application EP 1 069 211 A2 discloses aqueous acidic copper plating baths comprising a source of copper ions, an acid, a carrier additive, a brightener additive and a leveller additive which can be poly[bis(2-chloroethyl) ether-alt-1,3-bis[3-(dimethylamino)propyl]urea (CAS-No. 68555-36-2) which contains an organo-bound halide atom (e.g., covalent C—Cl bonds) in at least one terminus.
Urea polymers are known in the art from WO 2011/029781 A1 for the electrolytic deposition of zinc. Such polymers are made by a polyaddition of aminourea derivatives and nucleophiles. They are further known from EP 2 735 627 A1 as levellers for the electrolytic deposition of copper. However, the usage of such polymers as additives in copper pillar formation results in low pillar growth and an unfavorable pillar size distribution on a die (see examples, table 1). An in-homogeneous pillar size distribution may result in a lack of contact between the die and further components to which the die is assembled.
U.S. Pat. No. 8,268,157 B2 relates to copper electroplating bath compositions comprising a reaction product of diglycidylethers and nitrogen-containing compounds such as amines, amides, ureas, guanidines, aromatic cyclic nitrogen compounds such as imidazoles, pyridines, benzimidazoles, tetrazoles and so forth as levellers. Cyclic nitrogen compounds are preferred according to the teachings in this document (col. 6, I. 51), even more preferred are nitrogen containing heterocycles (col. 6, I. 53-54).
Polyethylenimines are widely used as levellers in copper electroplating baths because they are relatively convection independent. This convection independency is particularly important in copper pillar formation. A high convection dependency results in irregularly shaped pillars and an inhomogeneous pillar height distribution. However, polyethylenimines as levellers result in high amounts of organic impurities of copper deposits formed with copper electro-plating baths containing these polymers (see table 2). This is undesired in semiconductor applications as this leads to reduced copper or copper alloy grain sizes with more voids which then results in reduced overall conductivity of the copper or copper alloy layers formed.